Use percentage-based zoom

[junrrein]

It would be cool to have this.

Things to be determined:

Where should this be used?

I'm sure this would be a welcome addition to the "Big preview" window, but I don't know about using it in the main view, where small percentages will be the norm.

What does 100% zoom mean?

A PDF page doesn't have a size in pixels, but in physical units, and I'm not sure which units they are.

• poppler-cpp doesn't say anything about the units.
• poppler-glib doesn't either.
• poppler-qt5 says the dimensions are given in "points (i.e. 1/72th of an inch)".

Let's say we know the physical size of a page for certain (for an A4 format, it would be 210×297 cm). What would it mean to render it at 100% size? Do we need to take into account the DPI of the monitor, and then calculate the size in pixels that would match the physical size?

Looking around at what other projects do in this area (Evince, Okular) could provide the answer.